a) Field of the Invention
The invention is directed to an apparatus by which material can be partially removed from a workpiece by means of a milling cutter and a laser. An apparatus of this type is known generically from DE 199 10 880 A1.
b) Description of the Related Art
DE 41 13 633 A1 proceeds from a prior art in which workpieces which are to be worked by other machining methods in addition to laser machining are worked in different machining devices. The workpiece must be transported between machining devices and oriented to the tool in each machining device.
With the aim of providing a machining device by which, besides laser machining, other machining methods can be carried out without transporting or displacing the workpiece, DE 41 13 633 A1 suggests that two quills, one of which is provided for the laser head and the other for fastening another tool, communicate with a shared drive. Therefore, the same control unit can be used for carrying out machining processes.
The abstract to Japanese Patent Application JP 11114741 discloses a combination machining installation in which either a laser or mechanical tools such as drills and milling cutters, in particular also an end mill cutter, are used alternatively for machining workpieces. In order to use the different tools, the drill or the cutter is fastened directly to a spindle of a spindle head. To use the laser, a module is fastened to the spindle and, in this position, directs a laser beam to the workpiece in coaxial direction relative to the spindle, the laser beam being coupled in on the input side. All of the tools have the same working direction relative to the workplace because they are all oriented to the same spindle. Here also, the different machining methods can only be carried out successively with respect to time.
A machine tool for alternative working of workpieces either by laser radiation or by cutting tools is known from DE 199 10 880 A1. A milling head and a laser radiation source are jointly fastened to a headstock which is supported on an X-Y table and enables a horizontal movement of the tool relative to the workpiece. The laser radiation source is connected by a beam delivery channel to a laser head which is arranged laterally at the milling head. A scanner system which guides the laser beam over the workpiece surface in a focused manner is fastened to the laser head. Removal of material by layer is mentioned as a possible application of the machine tool. The individual machining methods are carried out successively in time in this case also.
It is known that special materials, e.g., ceramics or certain steels, can advantageously be removed by laser-assisted cutting. A laser beam partially heats the workpiece around a cutting zone to a temperature which facilitates cutting of the material. With laser-assisted turning of the workpiece on a lathe in which the workpiece is rotated and a cutting tool with only one knife is merely advanced, the laser beam is directed to the workpiece directly in front of the knife in the forward feed direction. This means that the laser beam maintains the same relative position with respect to the cutting tool during machining and can therefore be fixed relative to the cutting tool.
With laser-assisted milling, the heating of the cutting zone is more difficult, since a milling cutter usually has a plurality of tips, all of which simultaneously participate in the removal of material.
In the milling machine which is disclosed in DE 101 28 536 A1 and which can be used for laser-assisted milling of a three-dimensional surface, particularly a free-form surface, a laser device is arranged at an adjustable fastening so as to be swivelable around a spherical cutter.
To summarize: Basically two different groups of devices (machine tools) having a laser and a cutting tool are known from the prior art.
In devices of the first group in which cutting removal of material is assisted by heating with a laser, the laser radiation and a conventional chip-removing tool are used at the same time, and the laser radiation impinges on the workpiece outside of the instantaneous machining area of the chip-removing tool, i.e., for a milling cutter outside the outer circumference. Since the laser and the milling cutter work adjacent areas, the laser head and the milling cutter must also be positioned adjacent to one another.
In devices of the second group in which material is removed alternatively either by laser or by a cutting tool, the laser radiation and a conventional chip-removing tool are used successively with respect to time at the same machining location or at different machining locations. The machining methods proceed without influencing one another. When the machining method is changed in order to work at the same machining location, the position of the tools relative to the workpiece must be changed. Devices of this kind are used for multi-layer workpieces from which material must be partially removed over at least two layers of different materials. A chip-removing method is advantageous at least for the material of the first layer, and the material of the following layers can be advantageously removed with a cutting beam.
The devices which are known from and described in the prior art have the disadvantage that the lasers cannot begin until after the volume to be removed by milling has been removed (two work steps), i.e., the entire machining area must be gone over twice. The machining time (cycle time) is increased compared to a method in which the desired volume is removed by going over the entire machining area a single time (one work step).